linux-kernel - Re: Re: [PATCH 4/4] ASoC: wm8524: Delay some time to follow power up sequency

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Date:   Fri, 24 Feb 2023 12:30:43 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Chancel Liu <chancel.liu@....com>
Cc:     "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "ckeepax@...nsource.cirrus.com" <ckeepax@...nsource.cirrus.com>,
        "patches@...nsource.cirrus.com" <patches@...nsource.cirrus.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: Re: [PATCH 4/4] ASoC: wm8524: Delay some time to follow power up
 sequency

On Fri, Feb 24, 2023 at 10:54:59AM +0000, Chancel Liu wrote:
> > On Wed, Feb 22, 2023 at 07:39:45PM +0800, Chancel Liu wrote:

> > Doing a 100ms busy wait in atomic context does not seem like a great
> > idea, never mind a 1.5s one.  This shouldn't be done in trigger, it
> > needs to be done later - digital_mute() might be a better time to hook
> > in, though longer delays like this are really quite bad.

> Yes, such long time delay in driver is very bad. But this device requires
> waiting some time before able to output audio. We have to wait otherwise the
> beginning data may be lost.

It's not just that it's doing this in the driver, it's doing it in the
trigger() function which runs in atomic context.  That's unreasonable.

> The power up to audio out timing occurs after MCLK, BCLK and MUTE=1 are ready.
> I added the delay in trigger() because some CPU DAI drivers enable BCLK in
> trigger(). You suggested moving the delay to digital_mute(). It seems
> digital_mute() is called before cpu_dai->trigger. Please correct me if I'm
> wrong.

Hrm, right - in any case, it needs to be somewhere that isn't atomic
context.

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